Usually, commercial vehicles (HGV) such as semi-trailer tractors have a conventional HGV on-board main power supply that can supply typical automotive consumers up to a maximum power of around 1.5 kW. Electric consumers with higher power demand, such as air-conditioning units, therefore often require additional generators to provide electrical energy. Moreover, semi-trailers or commercial vehicle trailers equipped with electric units such as refrigerator units, concrete mixers, concrete pumps or shredders, etc., are also equipped with expensive power supply units such as electric generators which allow self-sufficient operation of the unit even when the trailer is parked and disconnected from the tractor machine. Such current supply units, for example with the power rating mentioned above, are extremely costly and not very well standardized.